The importance of the ability for public safety officials to communicate in public safety emergency situations is becoming increasingly important. These public safety officials may be associated with the fire department, police department, or any other public or private organization that is responsible for providing services related to safety of the public.
Conventionally, separate communications networks, i.e., public safety networks, provide service for these public safety communications. However, as is known from previous emergency situations, interference with communications over the public safety network can be caused by other cellular communications networks, e.g., cell phone networks, operating in the same geographic service area. Thus, due to this interference, critical public safety communications can be disrupted, which seriously degrades the ability of the public safety organization to respond.
This interference is generally a result of the use of traditional “high site transmission” communications networks, which are used for both public safety networks and other cellular networks. These traditional “high site transmission” networks are inherently flawed in that the strength of the signal received by a mobile communications device decreases as its distance from the network transmitter increases. Thus, the mobile device is susceptible to interference caused by relatively stronger signals from other carrier networks as it nears its outer-most boundary from the transmitting cell tower. FIGS. 1 and 2 illustrate a traditional high site transmitter architecture and the relationship between signal strength and susceptibility to interference based on distance from the transmitter in the traditional high site transmitter network, respectively.
In order to attempt to improve interference problems with non-public safety communications networks, fiber optic technology is increasingly being utilized. Optical fiber not only generally has increased transmission capacity over copper wire, but it is also generally more resistant to the effects of electromagnetic interference. FIG. 3 illustrates a network architecture for a cellular communications network 100. As can be seen, the cellular network consists of base transceiver stations (BTS) 110 which are connected to a mobile switching office (MSO) 120. The MSO is generally connected to the Public Switched Telephone Network (PSTN) 130. As is well-known, individual mobile units (MU) 140, which could be the individual subscribers' cell phones, communicate with the BTS when in the “cell” of the BTS.
Also shown in network 100 of FIG. 3 is a remote repeater node 150 that is connected to BTS 110. Repeater node 150 may be an optical repeater that is used in a distributed antenna system (DAS). The DAS node extends the coverage area of a cell. The DAS node is connected to the BTS and may be connected to the BTS by a fiber optic cable. Whereas only one DAS node is illustrated as being attached to one BTS, there may be many DAS nodes attached to a BTS. FIG. 4 illustrates the many DAS nodes that may be included in a distributed antenna system architecture. Thus, as can be seen in FIG. 5, with the DAS architecture, because the optical repeaters are distributed throughout the service area of the cell, the mobile device is not as susceptible to interference since the effective distance of the mobile device from the transmitter is not as great even in the most outer-boundary of the cell.
Whereas non-public safety communications networks may be taking advantage of fiber optics technology and distributed antenna system architectures, public safety networks are still stand-alone networks that utilize traditional “high site transmission” architectures. Therefore, there is a need for an improved architecture for a public safety network that can provide a greater degree of confidence in ensuring communications can be conducted in emergency situations.